Flash lamp



M. PIPKIN FLASH LAMP Filed Nov. 16, 1938 May 7, 1940.

Inventor retenait M.y`7,194o

UNITED STATES FLAvsn LAMP Marvin Pipkin, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application November 16, 1938, Serial No. 240,783`

3 Claims. (Cl. 67-31) My invention relates in general to flash lamps ofthe type used for. photographic purposes which usually comprise a sealed transparent bulb or envelope containing a readily combustible material. More particularly, my invention relates to the envelope or bulb of such ilash lamps.

At present, flash lamps generally comprise a sealed transparent bulb of clear glass in which is enclosed a readily combustible material, such as metal foil and/or Wire, together with suitable ignition means therefor, and a combustion-supporting substance, usually a gas filling, which, upon ignition of the lamp, enters into a reaction with the combustiblematerial with the resulting emission of actinic light- Lamp bulbs as a rule do' not have a uniform wall thickness. Flash lamps of the above-mentioned type develop internal pressure when flashed, and if there is a thin spot in the bulb Wall it may give way, resulting vin an explosion with consequent danger from flying fragments of glass. Accordingly, as a safeguard against such accidental explosions, it has been customary to provide the interior surface of the flash lamp 5 bulb with a lacquer coating such as cellulose l so that it tends to separate from the bulb Wall;

The presence of water vapor within the sealed' bulb likewise tends to separate the Ycoating from the bulb wall. Then too, the leakage of air into the bulb through cracks in the lacquered portion of the bulb wall results in a separation of the vcoating from the bulb wall. In any event, the separation of the lacquer coating from the bulb wall gives rise to a dangerous condition, for the separated portion of the inflammable lacquer coating burns freely when the lamp is flashed,

g thus tending to increase the pressure developed within thelamp and frequently causing an explosion. Also, the-hot molten particles of combustible material readilyl puncture the separated frequentlyA unawarev of its dangerous condition. According to the present invention,` means are provided to materially impede orretard the tendency of the lacquer coating to loosen or separate fromthe bulb wall,but if such a separation 5 actually should occur, a readily discerniblejndication thereof is promptly given.

.One object of my invention is to provide a flash lamp bulb with a rmly adherent lacquer coating on a surface thereof, preferably on the inner l0 surface.

4Another object of my invention is to provide a lacquered flash lamp bulb which will promptly give a readily discernible indication of any sepl aration of the lacquer coating from the surface of they bulb. I Still another object-of my invention is to provide a ash lampwith safety means' 'for positively indicating the leakage of air into said lamp through that portionof thelamp bulb. actually surrounding the combustible material within the lamp. y

A further object of my invention is toprovide an inside frosted flash lamp bulb having a coating 0f transparent lacquer on the frosted innerV sur- 25 face of said bulb. Further objects and advantages of my invention will appear from the following description of a species thereof and from the accompanying drawing, in which Fig. 1 is'an elevation, partly 30 in section, of a ash lamp comprising my invention; Fig. 2 is a fragmentary-sectional View, on an enlarged scale, of the lacquered bulb Wall portion Aof the flash lamp shown in Fig. 1; and Fig. 3 is an elevation of a iiash lamp comprising 35 ,my invention showing the visible indication given when a portion of the interior lacquer coating becomes separated from the lamp bulb.

Referring to Fig. -1, the fiash lamp according to'my invention comprises a vitreous transparent 40 envelope or bulb III containing a loose filling of combustible material II, such as a lamentary Wire of aluminum or its alloys, and a combustionsupporting gaseous filling, preferably oxygen. Mounted within the bulb I Il, within effective ignition range of the combustible material II, is a small filament I2 the ends of which are connected to leading-in Wires I3, I3-which extend through a stem I4 to a conventional screwthreaded lamp base I5. The lament I2 is em- 50 lacquer film and strike `the uncovered glass ofmdbedded in a bead I6of fulminating substance the bulb, thereby tending -to crack the same and cause an explosion. The separation of the 'lacquer film from the bulb -wall is diilicult to observe so that the person flashing the lamp is to thereby form the ignition means for the lamp. An insulating disc I1, preferably of asbestos, is mounted on the stem I4` to shield the base end of the lamp from the heat of combustion.

As shown particularly in Fig. 2, the inner sur-v face of the bulb l Il is frosted, preferably by etching, to thereby provide a roughened inner surface I8. This frosted surface is preferably produced by the method disclosed and --claimed inA my United States Patent Nox 1,687,510, issued October 16, v1928, although it may be produced by any other suitable method, such as by sand blasting. A thin coating I9 of a suitable clear lacquer, preferably cellulose acetate, is applied over the frosted inner surface I8 of the bulb I0. The' thickness of the coating may vary from 0.2 to 1 mil or thereabouts, but is preferably made 0.5 of a mil thick. The said coating I9 extends down into the neck portion of the lamp bulb to a point just beyond the insulating disc l1. Because of the roughened inner surface I8, the lacquer coating firmly adheres to the bulbmuch more so than is the case where the coating is applied to ordinary untreated glass bulbs. As a result, the danger of explosions, which frequently occur on the flashing of a lamp having a portion of the lacquer coating I9v separated from the bulb wall, is` practically eliminated.

The increased adherence of the lacquer coating to the bulb wall also materially reduces the number of lamps rejected during manufacture because of loosened bulb coatings. 'Ihe lamp bulb has a distinctive appearance in that the coated portion 'thereof has a clear glass appearance while the uncoated neck portion has the milkyA white appearance characteristic of frosted glass.

In addition to the above-enumerated advantages, safety indicating means are provided by the invention whereby the presence of any loosened or unattached lacquer coating material,

or the presence of air leakage into the bulb through the lacquered portions thereof, isrpositively and quickly indicated by the appearance of a readily discernible spot, as shown at 20 in Fig. 3, of milky white appearance corresponding to that of a conventional inside frosted lamp bulb. This spot of contrasting appearance defines the area of the inner bulb surface from which the lacquer coating has become loosened.` When the clear cellulose acetate solution is applied to the inside frosted lamp bulb Il), the original milky white' appearance of -the frosted bulb immediately disappears and becomes substantially transparent or clear. Apparently, this is due to the filling up of the cavities of the frosted inner surface I8 of the lamp bulb and the resulting formation, of a smooth interior surface which does not refract or diffuse the rays of light passing through the bulb Wall in the man- 4 ner effected by the original-frosted surface, but

instead transmits them substantially without refraction or diffusion. However, when any portion of the clear cellulose acetate coating loosens or becomes separated for any reason from the inner bulb surface I8, the uncovered surface of the bulb is again'ieft free` to refract and diffuse the. light passing through that portion of the bulb. Accordingly, an area of milky white appearance, lcorresponding to the original frosted appearance of the bulb and defining the area of the inner ybulb surface from which the cell lulose acetate coating has become separated, is instantly produced. This spot therefore serves to apprise one of the defectiveness of the lamp so that he will refrain from flashing the same and thereby prevent injury to person and property which might otherwise result if the lamp were flashed and an explosion occurred.

In the appended claims, the expression frosted inner surface is' intended to include all roughened. glass surfaces which. are similar to a surface frosted by etching, i. e., all surfaces having a multiplicity of minute pits or depressions. The term lacquer is also intended to include any similar protective coating material. Although it is preferred that the inner surface of the bulb be frosted and coated, the outer surface of fthe bulb may, if desired, be frosted and coated.

What I claim as new and desire to secure by Letters Patentof the UnitedStates is:

1.A flash lamp comprising a glass bulb containing a combustible material and combustionsupporting means, said bulb having a frosted surface, and a-protective coating of lacquer on said surface, kseparation of said lacquer coating from said surface being indicated by a con-A trasting appearance of said surface from its normalv appearance.

2. A dash lamp comprising Va glass bulb containing a combustible material and combustionsupporting means, said bulb having a frosted inner surface, and a protective coating of lacquer on said-inner surface, separation of said lacquer 1 coating from said surface being indicated by a MARVIN PIPKIN. 

